The present invention relates to environmental control systems for aircraft and, more particularly, to a modular air conditioning unit for supplying temperature-controlled air to an aircraft while on the ground.
Aircraft main engines not only provide propulsion for the aircraft, but in many instances may also be used to drive various other rotating components such as, for example, generators and pumps. The main engines may also be used to supply compressed air to the aircraft""s environmental control system, which may be used to supply temperature-controlled air to both the aircraft cabin and to electronic equipment within the aircraft.
When an aircraft is on the ground and its main engines are not being used, an alternative power source may be used to supply power for ground support operations. In addition, during some ground support operations, an external supply of cooling or heating air may be used to supply temperature-controlled air to the cabin and onboard aircraft equipment. For some type of aircraft ground support applications, most notably military aircraft ground support applications, a ground power cart may be used to supply electrical power to the aircraft and compressed air to an air conditioning system module. The air conditioning module in turn may supply temperature-controlled air to the aircraft cabin and the aircraft""s onboard electronic equipment.
One particular air conditioning system module that may be used during aircraft ground support operations receives high temperature (e.g., xe2x89xa7300xc2x0 F.) compressed air supplied by the ground cart, and conditions the compressed air to a predetermined temperature. The air conditioning system module may be used in at least two modes, a cooling mode, to supply cool air, or a heating mode, to supply warm air. To do so, the air conditioning system module may include a primary heat exchanger, a condenser, a moisture separator, and one or more cooling turbines. Typically, this air conditioning system module is designed so that when it is operating in the cooling mode it will supply cool air at a predetermined desired temperature for a given, predetermined design ambient temperature. For example, the system may be designed to supply cooling air at a temperature no higher than 55F when the ambient temperature is 125F. Thus, when actual ambient temperature is below the design ambient temperature, the air conditioning system may supply cooling air that is less than 55F.
In some instances, supplying air to an aircraft at less than 55F may not be desirable. Hence, the air conditioning system module may include a bypass flowpath that allows a portion of the high temperature compressed air to flow around the primary heat exchanger, and back into the cooler compressed air stream that is exhausted from the primary heat exchanger. For example, a valve may be installed in a bypass duct, and the valve may be positioned to control hot compressed air bypass flow rate, to thereby control the temperature exiting the primary heat exchanger, and in turn controlling the temperature of the air being supplied by the air conditioning system module.
Although the above-described system and method for controlling cooling air temperature to an aircraft during ground support operations is effective, it suffers certain drawbacks. For example, it can be difficult to consistently control the temperature of the cooling air by feeding a portion of the hot compressed air back into the compressed air that has been cooled. In addition, the cost of the air conditioning system module may be increased because high temperature ductwork and a high temperature valve may be needed to implement the compressed air bypass flow path.
Hence, there is a need for a system and method of providing temperature-controlled air to an aircraft environmental control system during ground support operations that does not use hot compressed air to control cooling air supply temperature when ambient temperature is below the maximum design temperature and/or is less costly than presently known systems and methods. The present invention addresses one or more of these needs.
The present invention provides a system and method of supplying temperature-controlled air to an aircraft environmental control system during ground support operations that is simple, efficient, and does not adversely affect system costs.
In one embodiment, and by way of example only, a temperature-controlled air supply system for use with a compressed air source and for connection to an aircraft on the ground includes a primary air flow passage, a bypass flow passage, a first heat exchanger, and a bypass valve. The primary air flow passage is coupled to receive a flow of primary air. The bypass flow passage is fluidly coupled in parallel with the primary air flow passage. The first heat exchanger has at least a first fluid flow path and a second fluid flow path. The first fluid flow path is fluidly coupled in series in the primary air flow passage, and the second fluid flow path is coupled to receive a flow of compressed air from the compressed air source. The first heat exchanger is adapted to transfer heat between the primary air and the compressed air and supply at least conditioned compressed air. The bypass valve is mounted on the bypass flow passage and is selectively moveable between a closed and an open position to control primary air flow rate through the bypass flow passage, whereby primary air flow rate through the first heat exchanger is controlled to thereby control conditioned compressed air temperature.
In another exemplary embodiment, a method of conditioning compressed air supplied from an aircraft ground support equipment includes supplying a flow of compressed air through a first heat flow path in a heat exchanger. A flow of primary air is supplied through a second flow path in the heat exchanger to thereby condition the compressed air to a temperature. A portion of the primary air is selectively diverted away from the second heat exchanger flow path to control primary air flow rate through the second heat exchanger flow path, whereby the temperature of the conditioned compressed air exiting the heat exchanger is controlled.